1. Field of the Invention
The present invention relates generally to a vibration damping device for installation between components to be linked in a vibration damping manner, and relates in particular to the vibration damping device having a first mounting member disposed spaced apart in the axial direction from a main rubber elastic body, and comprising a stopper mechanism for limiting relative displacement of the first mounting member and the main rubber elastic body when excessive load is input.
2. Description of the Related Art
Vibration damping devices of a design wherein a main rubber elastic body is disposed between a first mounting member and a second mounting member attached respectively to components to be linked in a vibration damping manner, are utilized in a wide range of fields. Japanese Patent No. 3362575 discloses, for example, one type of known vibration damping devices, wherein a first mounting member and a second mounting member are elastically coupled by means of a main rubber elastic body.
In some instances, a vibration damping device of this kind includes a rebound stopper for limiting relative displacement of the first mounting member and the second mounting member in direction of moving apart in the axial direction, in order to prevent excessive elastic deformation of the main rubber elastic body. However, even where a rebound stopper has been provided, there are still instances in which, owing to the size of the input load or the like, it is difficult to adequately limit relative displacement of the first mounting member and the second mounting member. In such instances, the main rubber elastic body may be forced to undergo excessive deformation, posing the risk of diminished durability of the main rubber elastic body.
Accordingly, JP-A-2005-23973 proposes a vibration damping device wherein the first mounting member is superimposed in the axial direction on the small diameter end face of a main rubber elastic body of generally frustoconical shape, and the second mounting member is affixed to the outer circumferential face of the large diameter end face of a main rubber elastic body, while a stopper mechanism is provided for a cushion-wise limitation of relative displacement of the first mounting member and the second mounting member in the direction of moving apart (rebound direction).
With this kind of vibration damping device, the first mounting member is superimposed in an unattached state against the main rubber elastic body and movable apart therefrom. In the event of an input load acting in the direction that causes the first mounting member to undergo relative displacement away from the main rubber elastic body in the axial direction, the first mounting member will undergo relative displacement away from the main rubber elastic body so that creation of tensile stress in the main rubber elastic body can be reduced or avoided altogether. Thus, improved durability of the main rubber elastic body is advantageously attained.
However, the inventors have found that a vibration damping device constructed in this way produces a new problem. The problem is caused by relative rotation of the first mounting member and a tubular bracket, for example. Specifically, where the vibration damping device is employed as an automotive engine mount, the first mounting member and the tubular bracket are fastened respectively by means of bolts or the like to a component on the power unit side and a component on the vehicle body side. At this time, the first mounting member and the tubular bracket are mounted while being positioned respectively with a specific orientation in the circumferential direction with respect to the components to be coupled in a vibration damping manner. However, with the structure of the vibration damping device taught in the aforementioned JP-A-2005-23973, the first mounting member and the main rubber elastic body furnished with the second mounting member fixedly mounted to the tubular bracket are formed independently of one another, and assembled in an unattached state so as to be movable apart from one another. This arrangement poses a risk that the first mounting member will undergo rotation relative to the tubular bracket during shipping or storage. Consequently, an operation to align the first mounting member and the tubular bracket in the circumferential direction with respect to the components to be linked becomes necessary before the first mounting member and the tubular bracket can be fastened to the components, resulting in insufficient ease of mount, and a risk of lower productivity of products (e.g. automotive vehicles etc.) in which the vibration damping device is installed.
In particular, where the mounting member is anisotropic due to the fact that the spring properties required thereof in the vehicle front-to-back direction differ from those required in the vehicle side-to-side direction, it will be necessary for the main rubber elastic body and the first mounting member to be aligned in the circumferential direction. However, with the vibration damping device structure taught in JP-A-2005-23973, wherein the main rubber elastic body and the first mounting member are capable of relative rotation, it is difficult to keep the main rubber elastic body and the first mounting member in the positioned state in the circumferential direction.
With the aim of preventing such rotation, there is proposed a method of disposing the axial distal end of a cushioning rubber so that it presses against the outer bracket in order to inhibit rotation. However, if the vibration damping device is subjected to outside force during shipping or the like such that the compressive force applied to the cushioning rubber becomes released, there is a risk first mounting member and the tubular bracket will be able to rotate relative to one another. Thus, it was difficult to consistently prevent relative rotation of the first mounting member and the tubular bracket by means of the cushioning rubber pressing against the tubular bracket in the axial direction.